In recent years, more rational packaging at lower cost has been demanded as well as miniaturization, mass production, and low cost, for electronic components such as semiconductor packages.
Packaging with trays is generally used for semiconductor packages and so on. Products are stored in the storage pockets of trays, the trays are stacked, and the stacked trays are bound. Then, the trays are put into an outer case such as a carton case, so that packaging is completed.
Such trays are broadly divided into a hard tray and a soft tray. A hard tray is formed by transfer mold. In this molding method, a plastic such as polystyrene or polypropylene is softened by heating, press-fit into a cope and a drag, and hardened therein. A complicated three-dimensional object can be formed with high stiffness and high accuracy.
A soft tray is formed by vacuum forming. In this molding method, a plate made of a plastic such as polystyrene is pressed to a die by pulling a vacuum between the die and one side of the plate while the plate is softened at a high temperature, so that the plate is bent. The processing accuracy of a soft tray is lower than that of a hard tray and thus a soft tray cannot form a complicated three-dimensional object. Further, a soft tray has a small thickness, resulting in low strength. However, a soft tray has advantages of a light weight and low cost. Moreover, highly inexpensive dies are available on short lead times, and thus a flexible response can be made.
For this reason, there is a vocal demand to use hard trays for semiconductor packages having external leads and electronic components requiring high accuracy and to use soft trays as much as possible for semiconductor packages having no external leads and electronic components not requiring high accuracy, in consideration of cost, delivery time, flexibility and so on.
Semiconductor packages are stored with main surfaces face up or stored with back surfaces face up. Thus, it is necessary to flip electronic components one by one according to the orientation and transfer the electronic components to another tray. For example, in the case of a surface-mounting semiconductor package of LGA, BGA, and so on, a main surface has a body of molded portions and a back surface has external terminals. Thus, electronic components are flipped one by one and transferred to another tray depending upon whether the main surface or the back surface is arranged face up. Hence, there is a particularly strong demand to avoid complicated operations.
A tray meeting the demand is disclosed in, for example, Japanese Patent No. 2852872. FIG. 9 is a simple illustration of this tray. FIG. 9A is a plan view showing the main surface of the tray. FIG. 9B is a plan view showing the back surface of the tray. FIG. 9C is a sectional view taken along line A-A of FIG. 9A. FIG. 9D shows stacked trays.
A tray 20 is a hard tray formed by transfer mold. First storing parts 21 are formed on the main surface of the tray and second storing parts 22 are formed on the back surface of the tray. The first storing parts 21 and the second storing parts 22 of similar size are formed on opposite positions of the tray. The four storing parts are arranged in two rows and columns in parallel.
In the first storing part 21, on the outer periphery of a rectangular storage pocket 23, a convex portion 24 is formed like a letter L along the corner of the storage pocket 23. Between the convex portions 24, a concave portion 25 is formed along the central portion of a side of the storage pocket 23. In the second storing part 22, on the outer periphery of a rectangular storage pocket 26, a convex portion 27 is formed along the central portion of a side of a storage pocket 26 so as to be engaged with the convex portion 24 and the concave portion 25 on the outer periphery of the first storage part 21. Between the convex portions 27, a concave portion 28 is formed like a letter L along a corner of the storage pocket 26. Ribs 29 extending along the thickness direction of the tray are formed on both edges of the convex portion 24 facing the storage pocket 23 and both edges of the concave portion 28 facing the storage pocket 26.
With this configuration, the inner surfaces of the convex portions 24 and 27 are brought into contact with the outer edges of an electronic component 30 to be stored in the storage pockets 23 and 26, so that the position of the electronic component 30 is regulated in the plane direction. Further, the ends of the ribs 29 are brought into contact with the outer edges of the main surface or the back surface of the electronic component 30 stored in the storage pockets 23 and 26, so that the position of the electronic component 30 is regulated in the height direction in the storage pockets 23 and 26.
As shown in FIG. 9D, when the trays 20 are vertically stacked, the convex portions 24 and the concave portions 25 of the first storing part 21 and the concave portions 28 and the convex portions 27 of the second storing part 22 are engaged with each other so as to position the upper and lower trays 20. The electronic components 30 are stored in the first storing parts 21 with the main surfaces face up and also stored in the second storing parts 22. By flipping the stacked trays 20, the electronic components 30 can be flipped at once and transferred to the second storing parts 22.
Generally, as an efficient positioning method for picking up an electronic component from a tray and mounting the electric component onto another electronic component, the outer edge of the electronic component is held and is transferred directly to another electronic component. In this method, the conventional tray 20 has the following problems in shape:
First, the convex and concave portions around the storage pockets 23 and 26 of the first storing part 21 on the main surface and the second storing part 22 on the back surface are considerably different from each other. The holding position of the electronic component 30 has to be changed between the first storing part 21 and the second storing part 22.
Second, in both of the first storing part 21 and the second storing part 22, each side has two boundaries of the convex portion 24 and the concave portion 25 or two boundaries of the convex portion 27 and the concave portion 28. Thus, the convex and concave portions have to be finely formed. Hence, when the electronic component 30 is small in size or the accuracy of processing the tray is low, the tray 20 cannot be produced. Even if the tray 20 can be produced, the concave portions 25 and 28 are small in size and thus the electronic component 30 cannot be picked up through the concave portions 25 and 28.
Further, in the conventional tray 20, when the electronic component 30 is supported in the first storing part 21, the L-shaped convex portions 24 are brought into contact with the corners of the electronic component 30 to regulate the position of the electronic component 30. However, when the electronic component 30 is supported in the second storing part 22, the flat convex portions 27 are brought into contact around the center of the electronic component 30 to regulate the position of the electronic component 30, resulting in a somewhat large rattle of the electronic component 30.
Another problem is that the tray 20 cannot be formed into a soft tray.
A soft tray cannot have different convex and concave portions on both sides like the tray 20. In a soft tray, the unevenness on a back surface is always similar to that of a main surface. By forming two soft trays, that is, by forming a first tray having a shape of a main surface and a second tray having a shape of a back surface, a structure similar to the tray 20 can be obtained. However, as described above, fine processing cannot be performed on a soft tray, and thus the foregoing three problems become more serious.
Moreover, in a soft tray, the unevenness of a back surface is always similar to that of a main surface but a shape displacement occurs according to a plate thickness. Hence, it is difficult to stack soft trays. When soft trays are stacked, it is difficult to pick up an electronic component interposed between the soft trays.
The present invention is devised to solve the problems, and has an object to provide a storing tray and a storing device whereby an object such as an electronic component to be stored can be picked up in a preferred manner and a plurality of stored objects can be flipped and transferred at once. The present invention has another object to form the storing tray as a soft tray.